Conventional front-lit illuminated microencapsulated electrophoretic displays characteristically reflect light in the white state in a so-called Lambertian manner. The light originating from a front light is radiated equally in all directions with equal luminance in the white state. Thus, a large portion of the reflected light is not reflected back to the viewer thereby limiting the perceived brightness of the display. This is inefficient by about a factor of two, of the perceived luminance to screen exitance where about 50% of the light is reflected away from the viewer.
The light output is different with conventional rear illuminated LCD displays where the emitted light is largely confined to approximately a 30° half-angle cone centered around a direction perpendicular to the plane of the front light. The illuminated LCD displays approximately doubles the ratio of perceived luminance to screen exitance for typical viewing angles. This roughly doubles the battery life. That is, the ratio of perceived luminance to screen exitance increases from 1/p, the value for Lambertian light, to roughly 2/p.
Therefore, in order for broader adoption of reflective displays by the public, there is a need for an improved front-lit, reflective displays having an increased ratio of perceived luminance to exitance which leads to a brighter display.